The question has been raised by xenobiologists before, if we do discover extraterrestrial life, will we know it when we see it?
Our solar system makes a tremendous model for what to expect of the galaxy, but not in the way we once thought. Once upon a time, and not so long ago, we thought our star system was a nice tidy little place. Four terrestrial worlds near the sun comprised of metals and silicates, four gas giants further out made mostly of hydrogen, helium, water and methane, etc.; nicely partitioned by an asteroid belt. Of course there was that odd man out, Pluto, but no biggie. Perhaps it was a fluke of creation.
The gas giants had many moons we learned, and once we started counting them we found more and more. We expected them to be largely dead, cratered and uninteresting places like our own Moon. Of course this is before we suspected the Moon had water deposits…
Missions like Pioneer, Voyager, Galileo and Cassini changed all that forever. No two moons are the same, and have widely different appearances, compositions, and geologic histories. On at least one there is active volcanism, and on others cryovolcanism. There are suspected subterranean oceans on the large moons orbiting Jupiter, and mysterious geyser vents on the outer edge of the solar system orbiting Neptune. Then there's Titan...
We now know Pluto was but the first of thousands of KBO’s, Kuiper Belt Objects, perhaps millions. Enigmatic places emerged from the blackness. Eris, Makemake, Haumea, Sedna, Orcus, Quaoar, and Vuruna…places that seemed more out of a science-fiction novel than real worlds, however far and remote.
And all this, orbiting one stable, type-G sub-dwarf star that is not particularly interesting or uncommon, given the spectrum of stellar objects we find out there, pun intended. My point should be obvious; all this in one little star system, and we know of at least 300 planets around nearby system, and counting. Most of these planetary models do not even remotely resemble the standard model we thought ours represented. Hot Jupiters, Super-Earths, 2nd and 3rd generation planets? Oh my, the galaxy is turning out to be a rather interesting place.
I sincerely believe our imagination is not up to the task. We should impose only the most realistic boundaries and restrictions on where we might find life, and then prepare to be massively surprised. The universe has been known to throw us more than a few curve balls.